Many imaging procedures in nuclear medicine use scintillation cameras, such as the Anger Camera, in conjunction with simple lead collimators or pinhole apertures. These systems have the following deficiencies:
(1) The collimator or pinhole is very inefficient in collecting the emitted radiation. Typically only about two out of every 10,000 emitted gamma-ray photons reach the detector.
(2) The spatial resolution is rather poor. The intrinsic resolution of the detector is about 4-8 mm, while the overall system resolution including the collimator is about 10-25 mm.
(3) The count-rate capability of the detector is very limited. Current cameras can handle only 50,000-100,000 detected photons per second without saturation or loss of spatial resolution.
Coded-aperture imaging is one avenue for alleviating the first problem. Coded apertures are much more efficient than pinholes and collimators, and even though they require more detected photons for the same signal-to-noise ratio, they still offer significant advantages over the conventional apertures in many clinical situations.
Unfortunately, coded apertures exacerbate the second and third problems listed above. To make effective use of coded apertures, the intrinsic spatial resolution of the detector must be better than is currently available. Also, there is no advantage in collecting more photons if the detector cannot process them.
In a preliminary search, the following prior U.S. patents were found, which appear to illustrate the present state of the art:
Martone et al, U.S. Pat. No. 3,769,509; PA1 Richey, U.S. Pat. No. 3,908,128; PA1 Coltman et al, U.S. Pat. No. 3,916,198; PA1 Stout, U.S. Pat. No. 4,058,727; PA1 Lijewski et al, U.S. Pat. No. 4,075,485; PA1 Barrett, U.S. Pat. No. 4,092,540; PA1 Lapidus, U.S. Pat. No. 4,093,857; PA1 Lange et al, U.S. Pat. No. 4,115,694; PA1 Lyons, U.S. Pat. No. 4,181,939;
Also of interest in the publication by M. A. Kujoory et al, "Coded Aperture Imaging of Gamma-Ray Sources with an Off-axis Rotating Slit", Applied Optics, Vol. 19, page 4186, Dec. 15, 1980.